Prior to the present invention, sealing devices of this kind, which are useful in sealing the piston of a working cylinder, have been disclosed in the art. See, for example, German Pat. No. DE 33 15 050 A1. This particular sealing device makes use of the excellent sliding and sealing properties of the PTFE plastic material, more commonly known as Teflon, for the sealing element. However, since this material, when used as the sealing element, is not sufficiently elastic, an elastic O-ring, installed in a groove of the piston, is used as an elastic support element to generate the necessary elastic pressure force for the sealing element and to ensure a sufficient seal. The sealing element in this prior art cylinder is constructed as a sleeve-shaped ring which rests directly on the elastic support. The center section of the sealing element is slightly bulged due to the pressure force of the support which is directed outward unto the sliding surface of the cylinder and functions as the sealing force so that a contact surface results. The dimensions of the contact surface remain undefined. An additional disadvantage of this device, known to the art, resides in the fact that the support must have some clearance in an axial direction within the groove holding it to allow for the change in the volume of the support as necessary for generating the elastic sealing force. A clearing of this kind, however, also signifies that the axial position of the support is not defined, or that the support acquires an undesirable axial mobility within the groove which hinders the exact positioning of the piston.
The disadvantages mentioned above, in relation to the device known to the art, can be avoided if a different sealing principle is applied, such as known from German Pat. No. DE 24 58 974 A1. In this device, known to the art, the piston in a working cylinder is encircled and sealed by a rubber cup packing. The packing of this seal, known to the art, advantageously forms two sealing edges which, due to their elastic material and the prestress resulting from it, are pressed against the sliding surface of the working cylinder. It is conceivable to coat this seal, known to the art, with a layer of PTFE plastic or a similar material with excellent sliding properties. However, a solution of this kind would cause design and production problems without assuring a sufficiently high elastic pressure force for the sealing edges.